<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <h1>点击按钮，看input是否被选中</h1>
    <input type="checkbox">足球
    <button id="select">all</button>
    <script>
    var input = document.getElementsByTagName("input")[0];
    // type = "checkbox"输入有checked属性，结果返回true,false
    var select = document.getElementById("select");
    select.onclick = function(){
        console.log(input.checked);
    }
    </script>
</body>
</html>